Traditionally the prior art has employed electromechanical devices such as a d'Arsonval galvanometer type of movement to convert an analog signal to a visual numeric indication. More recently in the prior art, cold cathode gas readout tubes have been employed such as the NIXIE tubes commercially available from Burroughs Corporation. This type of tube customarily has a common anode and a plurality of different metallic cathodes, each formed in the shape of a different numeral, alphabetic character, or symbol. The desired character is surrounded with a brilliant glow for providing a visual presentation when the corresponding cathode is energized. Unfortunately, however, cold cathode gas readout tubes are also subject to damage or malfunction due to shock or vibration in that it is essentially electromechanical in structure because the metallic cathodes in filamentary form are mechanically suspended and therefore susceptible to damage from severe shock or vibrational conditions. Additionally, this type of device requires a relatively high voltage of the order of 150 to 200 volts for its operation.
More recently liquid crystal techniques and devices have been employed for the presentation of digital, numeric, alphabetic, and symbolic information. Though liquid crystal techniques and devices obviate some of the disadvantages of other prior art devices, they suffer from the disadvantage that they are relatively expensive, and require complex circuitry for their operation, as well as a special order of voltages.
It is highly desirable in many applications to provide reliable, easy to read, relatively inexpensive means of presenting a digital readout of numeric or comparable information. Accordingly, there is environmental need for a new technique and type of device which will provide long life and reliable performance under extreme enviornmental conditions such as severe shock and vibration.